1. Field of Invention
This invention relates to an improved sorbent for removing NOx and SOx from exhaust gases and the improved removal process using that sorbent.
2. Description of the Previously Published Art
The NOXSO process, described in U.S. Pat. No. 4,798,711, uses a porous alumina sorbent containing sodium to adsorb NOx and SOx from flue gases. After the adsorption the nitrogen- and sulfur-laden sorbent is regenerated by heating the sorbent in a reducing atmosphere.
In addition to other preferred reducing atmospheres for regenerating, methane gas is also disclosed. However, by using natural gas or methane the regenerator operates at a higher temperature of about 650.degree. C. which tends to further reduce the surface area of the alumina beads.
As this NOXSO sorbent cycles back and forth from adsorption to regeneration, it undergoes transformations which reduce its surface area. In the fresh condition the alumina sorbent has a surface area on the order of about 200 m.sup.2 /g. After about 100 cycles the surface area of the sorbent is reduced to blow 50 m.sup.2 /g. When the surface area becomes that low, the performance becomes unacceptable.
3. Objects of the Invention
It is an object of this invention to develop a sorbent with a stable surface area and pore volume at regenerator conditions in the presence of sodium or other alkali metals.
It is further object of this invention to provide a stabilized surface area sorbent for use in adsorbing NOx and SOx from a flue gas.
It is further object of this invention to provide a sorbent with stable surface area under hydrothermal conditions in the presence of sodium.
It is further object of this invention to provide a sorbent with stable long term performance with regard to NO.sub.x /SO.sub.x adsorption after prolonged adsorption/regeneration cycling.
It is further object of this invention to provide a sorbent with low attrition characteristics upon adsorption/regeneration cycling.
It is further object of this invention to provide a sorbent which retains its integrity when it is in the bead form.
It is further object of this invention to provide alternative processes to produce a stabilized surface area sorbent for use in adsorbing NOx and SOx from a flue gas.
It is further object of this invention to provide a process for the continued removal of nitrogen oxides and sulfur oxides from a gas containing them with a stabilized sorbent which can undergo regeneration at high temperatures and under hydrothermal conditions.
These and further objects will become apparent as the description of the invention proceeds.